A. Technical Field
The present invention relates to a heat-exchanging method for an easily polymerizable compound. Specifically, the invention relates to a heat-exchanging method for easily polymerizable liquid compounds, such as (meth)acrylate esters, or easily polymerizable compound-containing liquids which method effectively prevents polymerization of the easily polymerizable compounds in heat exchangers.
B. Background Art
As to heat exchangers for heating and cooling of liquids, generally, shell-and-tube-type heat exchangers are used. However, in the case where the heat of liquids containing easily polymerizable compounds such as (meth)acrylic acid is exchanged using these shell-and-tube-type heat exchangers, polymerization of the easily polymerizable compounds occurs in the heat exchangers to lead not only to the deterioration of the heat exchangeability, but also to inside clogging of the heat exchangers, with the result that long-term stable operation becomes impossible.
The above polymerization in the shell-and-tube-type heat exchangers is considered to occur by the following mechanism. When heat is exchanged by running the easily polymerizable compound-containing liquid (which might hereinafter be referred to simply as xe2x80x9cliquidxe2x80x9d) to the shell side, a polymer forms at the liquid stagnant area which appears near a baffle plate, and then this polymer adheres to the outer surface of peripheral tubes. As a result, the heat conduction resistance increases to deteriorate the heat exchangeability. In addition, when the easily polymerizable compound-containing liquid is run to the tube side, a polymer similarly forms at the liquid stagnant area which appears in the channel, and then this polymer adheres to the inner surface of the tubes, resulting in the deterioration of the heat exchangeability. Furthermore, since the path is not single either at the shell or tube side, the liquid flow stagnates in polymer-adhered areas and, as a result, a chain growth of the adhered polymer occurs to lead to further deterioration of the heat exchangeability and finally to inside clogging of the heat exchanger.
Thus, in the case where the shell-and-tube-type heat exchanger is used, it is difficult to heat-exchange the easily polymerizable compound-containing liquid stably for a long period of time.
A. Object of the Invention
To solve the above prior art problems, the present invention has an object to provide a heat-exchanging method for an easily polymerizable compound which method effectively prevents polymerization of an easily polymerizable liquid compound or an easily polymerizable compound-containing liquid to enable a long-term stable heat exchange when the easily polymerizable liquid compound or the easily polymerizable compound-containing liquid is heat-exchanged.
B. Disclosure of the Invention
As is aforementioned, the deterioration of the heat exchangeability of the heat exchanger and the inside clogging of the heat exchanger, which are caused by the polymerization of the easily polymerizable compound in the heat exchanger, are triggered by: 1) the formation of polymer at the liquid stagnant area, 2) the attachment of this polymer to the heat transfer surface, and 3) the chain growth of the attached polymer.
The following have been found from the present inventors"" studies.
(1) For the prevention of the above factors 1) to 3) of the inside clogging of the heat exchanger, it is desired to singularize the liquid path and to decrease the liquid stagnant area in the heat exchanger as much as possible.
(2) Examples of single path heat exchangers include double-tube type heat exchangers and spiral type heat exchangers, but the former involve an extreme increase of installation space, therefore the latter spiral type heat exchangers are preferred for industrial use.
(3) Generally, the spiral type heat exchangers are classified into a vertical type and a horizontal type and, as to either type, two fluids for the heat exchange run through the single and rotary path, and the heat is exchanged by countercurrent flow. Incidentally, in the case where a fluid of small density such as steam or gas is used as a heating or cooling medium, an orthogonal current flow type vertical spiral heat exchanger to run the medium in an axial direction might be employed.
(4) As to a feature of the spiral type heat exchanger, the auto-cleaning function by energy of collision of a fluid with deposits to a spiral plate is known. Therefore, this heat exchanger is often used for heat exchange of a slurry-containing liquid which tends to cause troubles such as inside clogging of the heat exchanger. In addition, the horizontal type is assumed to generally have more auto-cleaning function.
(5) As to the heat exchange of the easily polymerizable compound-containing liquid, however, the tackiness of the formed and adhered polymer is so strong that the auto-cleaning function cannot sufficiently be exhibited upon the polymer that has adhered to the spiral plate.
(6) Therefore, for the prevention of the clogging during the heat exchange of the easily polymerizable compound, it is required to suppress the polymer formation in the heat exchanger and further to prevent the formed polymer from adhering to the spiral plate.
(7) In the prevention of the clogging with the slurry-containing liquid, the horizontal type has so far been assumed to be more effective. However, upon the easily polymerizable compound-containing liquid, rather the vertical type has been found to be more effective.
(8) In addition, for effective prevention of the polymerization in the heat exchanger to enable long-term stable operation, it is necessary that a vertical spiral type heat exchanger with a fluid path space of not less than 6 mm is used to carry out the heat exchange under conditions where the average liquid flow rate per unit sectional area of the path is not less than 0.2 m/sec, preferably in the range of 0.4 to 1 m/sec, and where the liquid residence time in the heat exchanger is not more than 100 seconds, preferably in the range of 60 to 15 seconds.
The present invention has been completed on the basis of the above findings.
That is, the present invention provides a heat-exchanging method for an easily polymerizable compound, in which a vertical spiral type heat exchanger with a fluid path space of not less than 6 mm is used as a heat exchanger to heat-exchange the easily polymerizable compound under conditions where the average liquid flow rate is not less than 0.2 m/sec and where the liquid residence time is not more than 100 seconds.
Incidentally, the average liquid flow rate and the liquid residence time are defined as follows.
Average flow rate (m/sec)={flow rate at inlet of spiral type heat exchanger (m3/sec)}/{path space (m)xc3x97path width (m)}
Residence time (sec)={heat transfer area (m2)xc3x97path space (m)}/{flow rate at inlet of spiral type heat exchanger (m3/sec)}
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.